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STOCKHOLDERS' EQUITY (Details 11) (Sales Agreement, USD $) | 12 Months Ended | 0 Months Ended
--- | --- | ---
Dec. 31, 2013 | Oct. 08, 2012 Maximum
Common Stock |  |
Aggregate offering price of common stock |  | $ 50,000,000
Maximum commission rate (as a percent) |  | 3.00%
Sales Agreement |  |
Lock-up period | 60 days |

X
- Definition Represents the aggregate offering price for which the entity may elect to issue and sell shares of its common stock under the sales agreement. + References No definition available. + Details
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Namespace Prefix: | gern_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the duration of the lock-up period following the underwritten public offering. + References No definition available. + Details
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Namespace Prefix: | gern_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the percentage of maximum commission rate, based on gross proceeds of sale price per share of common stock sold through MLV & Co. under the sales agreement. + References No definition available. + Details
Name: | gern_MaximumCommissionRate
Namespace Prefix: | gern_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | gern_SalesAgreementAbstract
Namespace Prefix: | gern_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_ClassOfStockLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration